Method and apparatus for measuring electromagnetic radiation

ABSTRACT

An apparatus and method wherein the capacitance of a semiconductor junction subjected to an electromagnetic radiation field is utilized to indicate the intensity or strength of the electromagnetic radiation is described.

United States Patent 1191 Been July 10, 1973 METHOD AND APPARATUS FOR3,173,091 3/1965 Strull 250/833 R MEASURING ELECTROMAGNETIC gg RADIATION3,598,997 8/1971 Baertsch [75] Inventor: Julian F. Been, Medina, Ohio2,155,509 4/ 1939 Schroter V 2,839,678 6/1958 DeWitz.

[73] Ass1gnee: The United States of Amer ca as 2,862,416 12/1958 Doylerepresented by th Administrator of 2,963,576 12 1960 Enikeiefi" 250/833R theNational Aeronautics and Space Washington Primary Examiner-HermanKarl Saalbach [22] Filed: Jan. 6, 1971 Attorney-N. T. Musial, J. A.Mackin and John R.

[21] Appl. No.: 104,346 Manning [52] US. Cl ..250/336, 307/308 [57]ABSTRACT [51] Int. Cl .1 ..G01t 1/24, H01] 15/00 58 Field 61 Search250/833 R; aPParaws and methd capacltance of 324/60 B 61 317/234 asemiconductor junction subjected to an electromagnetic radiation fieldis utilized to indicate the intensity [561 References Cited or strengthof the electromagnetic radiation is de- UNITED STATES PATENTS 3,l73,09]3/1965 Perlman et al 317/234 3 Claims, 1 Drawing Figure BRID'GEI BALANCEDETECTOR -1 EILECTRO MAGNETIC Patent ed July 10, 1973 mvemon JULIIAN F.BEEN ATTORNEYS METHOD AND APPARATUS MEASURING ELECTROMAGNETIC RADIATIONORIGIN OF THE INVENTION The invention described herein was made byemployees of the United States Government and may be manufactured andused by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

BACKGROUND OF THE INVENTION This invention relates to measuringinstruments and is directed more particularly to a method and apparatusfor measuring electromagnetic radiation.

Up to the present time, one of the most common ways of measuring gammaradiation emitted from radioactive materials has been to utilize anionization chamber system. Such systems require relatively high voltage,have considerable background noise, and are expensive because of thepower "supplies, high voltage cabling and instrumentation which must beincorporated in such a system. Furthermore, even miniaturetype ionchambers are often larger than desired for use in nuclear reactor work.

Some devices have been constructed which utilize semiconductor diodes tomeasure gamma radiation. However, these devices are generally based uponthe change of conductance or photovoltaic effect of the diode as afunction of electromagnetic radiation intensity. Because the conductancephotovoltage and photocurtent of a diode do not change linearly withrespect to the change in strength of electromagnetic radiation,complicated correction and calibrating circuits must be provided.

As is well known, visible light has been measured in the past bylightmeters. Such instruments use a semiconductor junction which generates avoltage when subjected it) visible light.

OBJECTS AND SUMMARYOF THE INVENTION It is an object of the invention toprovide a new and novel semiconductor electromagnetic radiationmeasuring device. i

Itis another object of the invention to provide an apparatus and methodfor utilizing a relatively linear characteristic of a semiconductorjunction to measure electromagnetic radiation.

Still another object of the invention is to provide a method andapparatus which utilizes a-c in measuring and detecting sections of theapparatus to minimize background noise. t

It is another object of the invention to provide a method and apparatusfor accurately measuring electromagnetic radiation in a field which mayalso include neutrons.

In summary, the inventive method and apparatus accurately measureelectromagneticradiation without excessive background noise and in thepresence of neutrons and at low cost.

DESCRIPTION OF THE DRAWINGS The single FIGURE is a schematic diagram ofapparatus embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT measuring section 11. Thedetecting section comprises a semiconductor junction such assemiconductor diode 12 which has a P-N junction. The cathode and anodeof the diode 12 are connected via signal carrying leads 13 and 14 intoonearm of a bridge 19. Where the radiation to be measured consists ofgamma rays or X-rays, a light-tight housing 15 may enclose the diode 12.The housing 15 may be either plastic or metal. However, if a metalhousing 15 is used, those skilled in the art of gamma and X-rays willrealize that various metals and different thicknesses of metals may beutilized to construct the housing 15 so that certain desired wavelengthsmay be filtered or blocked. For example, aluminum, beryllium andtitanium will block all visible and ultraviolet light but will transmitsoft and hard X-rays.

To prevent undesirable background noise from being added to the signalon the leads 13 and 14, shields l6 and 17, respectively, are providedfor those leads. The shields 16 and 17 are grounded as at 18.

As indicated previously, the diode 12 is connected into one arm of abridge 19. A second arm of the bridge 19 includes a variable capacitor20 while third and fourth arms include secondary windings 21 and 22,respectively. Primary windings 23 and 24 impress high frequencyalternating current from the a-c signal generator 25 on the secondarywindings 21 and 22, respectively. The alternating signal must be smallenough so that the diode 12 is not forward biased to any significantextent.

Todeterrnine when the bridge 19 is balanced, that is when thecapacitanceof diode 12 is equal to the capacitance of variable capacitor20, a bridge null or balance detector such as a meter 26 is connectedfrom a point between first and second arms to a point between the thirdand fourth arms of the bridge. This latter point is grounded.

In accordance with the method of the invention, the diode 12 is placedin an electromagnetic radiation field, such as a gamma field which mayinclude neutrons. The capacitor 20 is then adjusted to obtain balance ofthe bridge 19 at which point the capacitance of capacitor 20 is equal tothe capacitance of a diode 12. Therefore, if thccapacitance of the diode12 is known for an electromagnetic radiation field of a certainintensity, then the capacitance reading is a direct measurement of thestrength of the electromagnetic radiation. Thusit will be seen, that bysubjecting the diode 12 to knownelectromagnetic radiation fields thecapacitor 20 may be calibrated to read directly in any desired units ofelectromagnetic radiation field strength measurements. Advantageously,the capacitance of the junction of the diode 12 is directlyproportional, for particular ranges, to the amount of ionizing radiationto which it is sub jected. Accordingly, calibration of the radiationmeasuring device embodying the invention is very simple andstraightforward. From the foregoing it will be seen that the inventionprovides a measure of magnetic radiation intensity by measuring arelatively linearly varying disk characteristic as a function ofelectromagnetic radiation field strength. That device is alsoinexpensive and is not sensitive to background electrical noise.

It will be understood that changes and modifications may be made to theforegoing invention by those skilled in the art without departing fromthe spirit and scope of the invention as set forth in the claimsappended hereto.

What is claimed is:

l. A gamma radiation measuring device comprising:

a semiconductor device at least one p-n junction;

a light-tight metal enclosure disposed around said semiconductor device,said metal being selected from the group consisting of aluminum,beryllium and titanium;

an A-C capacitance bridge; and

signal carrying means connecting said last named means to said p-njunction of said semiconductor 5 device whereby the capacitance of saidone junction of said semiconductor device may be measured when saidsemiconductor is subjected to gamma radiation to indicate the intensityof said gamma radiation. 2. The radiation measuring device of claim 1wherein said semiconductor device is a diode.

3. A method of measuring gamma radiation compris- 5 ing the steps of:

disposing a p-n junction in a gamma field of unknown strength;

measuring the capacitance of said junction with an AC capacitance bridgeto obtain a measurement of the known field strength;

shielding said junction from electromagnetic radiation of apredetermined range of wave-lengths;

disposing said junction in a gamma field of unknown strength; and

measuring the capacitance of said junction with an a-c capacitancebridge to determine the magnitude of gamma radiation of said field ofunknown strength.

1. A gamma radiation measuring device comprising: a semiconductor deviceat least one p-n junction; a light-tight metal enclosure disposed aroundsaid semiconductor device, said metal being selected from the groupconsisting of aluminum, beryllium and titanium; an A-C capacitancebridge; and signal carrying means connecting said last named means tosaid p-n junction of said semiconductor device whereby the capacitanceof said one junction of said semiconductor device may be measured whensaid semiconductoR is subjected to gamma radiation to indicate theintensity of said gamma radiation.
 2. The radiation measuring device ofclaim 1 wherein said semiconductor device is a diode.
 3. A method ofmeasuring gamma radiation comprising the steps of: disposing a p-njunction in a gamma field of unknown strength; measuring the capacitanceof said junction with an AC capacitance bridge to obtain a measurementof the known field strength; shielding said junction fromelectromagnetic radiation of a predetermined range of wave-lengths;disposing said junction in a gamma field of unknown strength; andmeasuring the capacitance of said junction with an a-c capacitancebridge to determine the magnitude of gamma radiation of said field ofunknown strength.